Dual power brake booster and method of generating brake actuating pressure

Abstract

A vehicle brake booster and master cylinder assembly has a vacuum suspended booster section which is controlled by movement of the vehicle brake pedal. A hydraulic booster section is in series with the vacuum suspended booster section, and a master cylinder unit is in series with the hydraulic booster section. The assembly is so arranged that in normal operation the vehicle operator obtains boosted brake actuating pressures by operation of the vacuum suspended booster which acts through the hydraulic booster mechanism without operating the hydraulic booster. When greater brake actuating pressures are required, as indicated by increased brake pedal force exerted by the operator, the vacuum booster reaches its limit or runout condition and the hydraulic booster is operated so as to continue the increase in master cylinder output pressure. If still further master cylinder output pressure is required when the hydraulic booster has reached its runout condition, the master cylinder is actuated manually through mechanical force transmitting elements which are parts of the booster sections. The vacuum suspended booster section is connected to the vehicle engine intake manifold as a vacuum source, and the hydraulic booster section is connected in the hydraulic power steering gear system so that hydraulic pressure for its operation is generated by the power steering gear pump. The assembly is so interconnected that the master cylinder can be operated maually when there is no or insufficient power pressure to operate either booster section. It may also be operated by actuating the vacuum suspended booster section, and, when no hydraulic pressure is available to the hydraulic booster section, this operation may be followed by manual actuation. It may be operated by initially actuating the hydraulic booster section when there is no vacuum available for initially operating the vacuum suspended booster section, followed by manual actuation as needed. In one embodiment the assembly utilizes a single hydraulic fluid for the hydraulic booster section and for the master cylinder and brake apply circuitry. In another embodiment the hydraulic booster section is operated by a separate fluid circuit which is fluidly independent of the master cylinder and brake apply pressure circuitry.

We claim: 
     
       1. A brake booster system having a wheel cylinder actuating member and first and second booster sections sequentially operable to sequentially operate said wheel cylinder actuating member, said first and second booster sections being respectively defined by first and second power boosters and effective for manual operation of said wheel cylinder actuating member upon runout of both of said boosters, said system comprising in combination: a manually movable input member;   said first power booster having a housing into which said input member extends, a pair of booster output force transmitting output elements extending out of said housing and movable in follow-up moving relation to said input member and effective under normal power boost operation of said wheel cylinder actuating member by said first power booster to move in unison with said input member, one of said pair of output elements being effective to have relative movement in relation to said input members only when a first power booster runout condition exists;   said second power booster having a housing;   said pair of output elements also being part of said second power booster and extending into said second power booster housing from said first power booster and providing a pair of input control elements for said second power booster within said second power booster housing effective in follow-up moving relation to said input member only upon said runout relative movement to condition said second power booster for power boost operation;   said wheel cylinder actuating member being operatively connected with at least one of said pair of output elements to be responsive to movements of said input member.   
     
     
       2. A brake booster system having a wheel cylinder actuating member, an output member and first and second booster sections respectively defined by first and second power boosters actuatable in series on said wheel cylinder actuating member through said output member, said system comprising in combination: a manually movable input member;   said first power booster having a housing into which said input member extends, a pair of parallel-acting booster output force transmitting booster output elements extending out of said housing and movable in follow-up moving relation to movement of said input member and effective under normal power booster operation of said wheel cylinder actuating member by said first power booster to move in accordance with movement of said input member, one of said elements being moved by said input member to be effective to have relative movement in relation to the other of said elements only when said first power booster is conditioned for power operation of said wheel cylinder actuating member to a predetermined extent;   said second power booster having a housing out of which said booster system output member extends;   said pair of output elements also defining part of said second power booster and extending into said second power booster housing from said first power booster and including a pair of second power booster input elements within said second power booster housing and effective only upon the relative movement between said pair of output elements to actuate said second power booster in follow-up moving relation to said input member;   said wheel cylinder actuating member being operatively connected with at least one of said pair of elements through said output member to be operatively responsive to movement of said input member.   
     
     
       3. A power booster assembly comprising: a master cylinder unit;   first and second power booster units each having a housing;   said first booster unit having a pair of parallel-acting booster output force transmitting output members extending outwardly of its housing and capable of concurrent and relative movements, and one movable input member;   said second booster unit having a pair of parallel-acting first booster unit output force transmitting input members extending into its housing from said first booster unit and formed as operative parts of said pair of parallel-acting output members of said first booster unit and therefore also being capable of concurrent and relative movements, and one movable output member extending outwardly of said second booster unit housing and connected to transmit actuating force to said master cylinder unit, said second booster unit being conditioned for power boost operation of said master cylinder unit only up on relative movement of its input members and said first booster unit being conditioned for power boost operation of said master cylinder unit only while there is no relative movement of its output members.   
     
     
       4. A power booster assembly comprising: a master cylinder unit;   first and second power booster units each having a housing;   said first booster unit having a sleeve and a plunger in said sleeve defining a pair of parallel-acting booster output force transmitting output members extending outwardly of said first booster unit housing and capable of concurrent and relative movements, and one movable input member extending into said first booster unit housing;   said sleeve and plunger of said first booster unit also extending into said second booster unit housing and forming a part of said second booster unit and defining a pair of parallel-acting first booster unit output force transmitting input members for said second booster unit, a valve seat and a mateable valve member being respectively movable with the portions of said sleeve and plunger forming said second booster unit input members, and one movable output member extending from said second booster unit housing and connected to transmit actuating force to said master cylinder unit, said second booster unit being conditioned for power boost operation of said master cylinder unit only upon relative movement of its input members and said first booster unit being conditioned for power boost operation of said master cylinder unit only while there is no relative movement of its output members.   
     
     
       5. A brake booster and master cylinder assembly comprising: a differential air pressure powered booster section having a housing;   a hydraulic pressure powered booster section in operative series therewith and having a housing;   a master cylinder section in operative series with said booster sections to be operated thereby;   manual force input means controlling the actuation of said booster sections and providing for manual operation of said master cylinder section;   each of said booster sections being power operable independently of power operation of the other, with one of said booster sections being conditioned for its full range of power operation of said master cylinder section by said manual force input means in sequence with and only subsequently to the conditioning for the full range of power operation of said master cylinder section of the other of said booster sections by said manual force input means, said manual force input means manually operating said master cylinder section only after both of said booster sections have been conditioned for their full range of power operation;   and force transmission members extending outwardly of said first booster section housing and into said second booster section housing and adapted for concurrent and relative movement with respect to each other and interconnecting said booster sections and effective only upon said relative movement to condition said hydraulic pressure powered booster section for power operation of said master cylinder section and only when a power runout condition exists in said differential air pressure powered booster section.